The present invention relates to communication systems, and more particularly to a satellite communication system utilizing a linear block coding technique.
Satellite communication systems have emerged as a viable solution for supporting broadband services. As such, power and bandwidth efficient modulation and coding are highly desirable for satellite communications systems to provide reliable communication across noisy communication channels. These communication channels exhibit a fixed capacity that can be expressed in terms of bits per second (bps) per Hz (bps/Hz) for a given signal-to-noise ratio, defining a theoretical upper limit (known as the Shannon limit). As a result, coding design has aimed to achieve rates approaching this Shannon limit. One such class of codes that approach the Shannon limit is Low Density Parity Check (LDPC) codes.
Traditionally, LDPC codes have not been widely deployed because of a number of drawbacks. One drawback is that the LDPC encoding technique is highly complex. Encoding an LDPC code using its generator matrix would require storing a very large, non-sparse matrix. Additionally, LDPC codes require large blocks to be effective; consequently, even though parity check matrices of LDPC codes are sparse, storing these matrices is problematic. From an implementation perspective, storage is an important reason why LDPC codes have not become widespread in practice. A key challenge in LDPC code implementation has been how to achieve the connection network between several processing engines (nodes) in the decoder.
The explosive growth of broadband services has been fueled by consumers"" demands for greater and greater data rates to support, for example, their multi-media applications (e.g., streaming video, web surfing, etc.). Therefore, communication service providers require an infrastructure that can support high data rates, particularly in bandwidth-constrained systems. Higher-order modulation techniques that carry more than two bits per symbol, such as 8-PSK (Phase Shift Keying) and 16-QAM (Quadrature Amplitude Modulation), can provide more efficient bandwidth utilization. Unfortunately, conventional LDPC communication systems utilize a modulation scheme that carries binary or quaternary modulation whose signal waveforms representing the information are either binary anti-podal, or orthogonal to each other.
Therefore, there is a need for a satellite communication system that employs simple encoding and decoding processes, while minimizing cost. There is also a need for using LDPC codes efficiently to support high data rates, without introducing greater complexity. There is also a need to improve power and bandwidth efficiencies in a bandwidth constrained system, such as a satellite communication system.
These and other needs are addressed by the present invention, wherein an approach is provided for communicating over a satellite communication system utilizing structured Low Density Parity Check (LDPC) codes in conjunction with high order modulation schemes having signal constellations with two or more symbols represented by a signaling point. Structure of the LDPC codes is provided by restricting the parity check matrix to be lower triangular. The approach can advantageously exploit the unequal error protecting capability of LDPC codes on transmitted bits to provide extra error protection to more vulnerable bits of the high order modulation schemes (such as 8-PSK (Phase Shift Keying) and 16-QAM (Quadrature Amplitude Modulation). The above approach provides a bandwidth and power-efficient modulation techniques that are well suited for direct broadcast satellite or broadband satellite communications. Depending on the overall system link parameters, the approach can achieve high power efficiency and/or bandwidth efficiency, with simple decoding hardware, which is capable of high-speed operation.
According to one aspect of an embodiment of the present invention, a method for reliably communicating over a satellite in support of a communication service is disclosed. The method includes encoding an input message to output a structured Low Density Parity Check (LDPC) coded message. The method also includes modulating the coded message according to a high order modulation scheme, and transmitting the modulated signal over the satellite.
According to another aspect of an embodiment of the present invention, a satellite terminal for reliably communicating over a satellite in support of a communication service is disclosed. The terminal includes an encoder configured to output a structured Low Density Parity Check (LDPC) coded message in response to an input message. The terminal also includes a modulator configured to modulate the coded message according to a high order modulation scheme, wherein the modulated signal is transmitted over the satellite.
According to another aspect of an embodiment of the present invention, a satellite communication system supporting a communication service is disclosed. The system includes a first terminal configured to encode an input message to output a structured Low Density Parity Check (LDPC) coded message, and to modulate the coded message according to a high order modulation scheme, wherein the modulated signal is transmitted over a satellite. Also, the system includes a second terminal configured to receive the transmitted signal via the satellite.
According to another aspect of an embodiment of the present invention, a system for reliably communicating over a satellite in support of a communication service is disclosed. The system includes means for encoding an input message to output a structured Low Density Parity Check (LDPC) coded message, and modulating the coded message according to a high order modulation scheme that has a signal constellation representing more than two symbols per signaling point. The system also includes a transmitter configured to propagate the modulated signal over the satellite.
Still other aspects, features, and advantages of the present invention are readily apparent from the following detailed description, simply by illustrating a number of particular embodiments and implementations, including the best mode contemplated for carrying out the present invention. The present invention is also capable of other and different embodiments, and its several details can be modified in various obvious respects, all without departing from the spirit and scope of the present invention. Accordingly, the drawing and description are to be regarded as illustrative in nature, and not as restrictive.